Shifts in microbial community functions and nitrifying communities as a result of combined application of copper and mefenoxam.

In this microcosm study, we focused on the effect of a combined application of copper and mefenoxam on the functional diversity of soil microbial communities. Treatments with combined and separate applications of copper and mefenoxam were sampled at 24 and 60 days and control soil was sampled at 0, 24 and 60 days. Structural and metabolic profiling of microorganisms were performed by arbitrarily primed (AP) and RNA arbitrarily primed-PCR (RAP-PCR). Cluster analysis resulted in separate grouping of AP and RAP-PCR profiles, with differences between control and treatments being more pronounced with respect to RAP-PCR profiles. amoA, a functional molecular marker for beta-subgroup ammonia-oxidizing bacteria, could only be detected at day 60 in treatments of mefenoxam, and mefenoxam+copper, with higher gene copies in the latter. There was also an increase in potential nitrification activity on application of mefenoxam and mefenoxam+copper. Comparison of amoA diversity was performed by denaturing gradient gel electrophoresis followed by construction of a clone library of amoA fragments amplified from the mefenoxam+copper-treated sample. Analysis of clones was performed by restriction digestion and subsequent sequencing. Patterns 1 and 5 were seen in 93% of the clones and clustered together with amoA sequences of Nitrosospira, indicating that Nitrosospira-like organisms are the major nitrifiers under mefenoxam treatments.

Changes in soil chemical properties and microbial activities in response to the fungicide Ridomil Gold plus copper.

The purpose of the study was to investigate changes of soil chemical and biological properties changes resulting from a single application of the fungicide Ridomil Gold plus copper (Ridomil Gold plus)(mefenoxam 6% + copper oxide 60%) at the following rates 0.25, 0.5, 1, 2, and 10 g m(-2). Selected chemical properties generally differed between fungicide rates over longer incubation periods. Microbial activity indices (available N, ammonification rates and specific enzymatic systems) were more sensitive indicators of change. Values of these indicators generally increased with incubation period and decreased or increased at high rates. Significant changes in P availability occurred after 90 days of incubation at rates > or = 1 g m(-2). Incorporation of the fungicide significantly increased NH4+ levels in soil after 75 days of incubation. These changes stimulated soil microbial activity as evidenced by increased ammonification rates especially at long-term exposure. Of the enzyme activities studied, dehydrogenase and beta-glucosidase activities were the most sensitive to ridomil gold plus. This sensitivity was more pronounced with the dehydrogenase activity.